FIG. 1 depicts a schematic diagram of a portion of a typical wireless telecommunications system in the prior art. Such a system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals 101-1 through 103-1) that are situated within a geographic region.
The heart of a typical wireless telecommunications system is Wireless Switching Center ("WSC")120, which may also be known as a Mobile Switching Center ("MSC") or a Mobile Telephone Switching Office ("MTSO"). Typically, WSC 120 is connected to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system. Additionally, WSC 120 is connected to local- and toll-offices (e.g., local-office 130, local-office 138 and toll-office 140). WSC 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially-distinct areas called "cells." As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on terrain topography. Typically, each cell contains a base station, which comprises radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with WSC 120.
As an example of wireless telecommunications, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to WSC 120. Upon receiving the information, and with the knowledge that it is intended for wireless terminal 101-2, WSC 120 then returns the information to base station 103-1, which relays the information, via radio, to wireless terminal 101-2.
The wireless telecommunications described above occur over a plurality of communication channels. Such channels are characterized by a carrier frequency, and a bandwidth (e.g., 30 kHz) over which the carrier frequency is modulated to carry information content. Wireless service providers license, at a very substantial cost, a band of frequency spectrum sufficient to provide an adequate number of communication channels for supporting communications within a given wireless system.
The amount of spectrum that a provider must obtain to support such communications is predominantly a function of (1) the amount of spectrum that a channel consumes, (2) the extent to which channels used in any one of the cells can be reused in other cells, (3) the call traffic ("call demand" or "traffic demand") on the system, and (4) the acceptable percentage of blocked call attempts. Regarding (2), channel reuse is limited by channel interference. Such interference, which may occur between cells ("co-channel interference") and between numerically-consecutive or nearly-consecutive carrier frequencies ("adjacent-channel interference"), must be kept within acceptable limits.
Since spectrum is very expensive, it is disadvantageous for a provider to license substantially more spectrum than is required for supporting communications within its wireless telecommunications system. As such, it would be advantageous to have a good estimate of that spectrum requirement. Unfortunately, little guidance is available for estimating the spectrum requirements for a wireless telecommunications system. One reason for the dearth of information on the subject may be the difficulty of estimating such requirements, which may be abstracted as a generalization of the notoriously difficult problem of graph "coloring." In fact, frequency spectrum estimation adds an additional degree of complexity to the already complicated standard graph coloring problem.